1) Field of the Invention
The present invention relates to a liquid adhesive for electronic parts to be used for adhering between parts around a leadframe making up a semiconductor device, e.g., lead pins, semiconductor chip-mounted substrates, heat spreaders, semiconductors themselves, and to a process for forming an insulating adhesive layer using the same.
2) Description of the Related Art
Conventionally, adhesive tapes for innerlead lock of leadframe, TAB tapes, etc., are used as adhesive tapes for use in the interior of resin-sealed type semiconductor devices. For example, the adhesive tapes for innerlead lock of leadframe have been used to fix lead pins of the leadframe in order to increase the yield of production and to enhance the efficiency for producing a leadframe itself and the whole semiconductor assembly stages, as shown in FIG. 1. In general, a leadframe manufacturer a leadframe, and brings to it a semiconductor manufacturer, at which a chip is mounted thereon followed by molding the leadframe with a resin. In FIG. 1, the symbol (a) shows a whole drawing, and (b) shows a partly enlarged view, in which numerical 1 is a position of innerlead lock, 2 is a dam bar, 3 is a lead pin, and 4 is an island portion. For this reason, it has been required for the adhesive tapes for innerlead lock of a leadframe not only to possess general reliability in a level required for semiconductor and enough processability at the time of taping, but also to possess sufficient adhesive strenght immediately after taping and heat resistance enough for withstanding thermal process at the stages of assembling semiconductor devices.
Conventionally, the adhesive tapes for use in such an application include adhesive tapes applying on a support film of a polyimide film, etc., an adhesive comprising a synthetic rubber resin such as plyacrylonitrile, polyacrylate or acrylonitrile-butadiene copolymer solely, or modified with any other resin or blended with any other resin to come into a B-stage.
In recent years, in the interior of the semiconductor device, the package structure has become complicated due to the increased number of pins and the need to secure the radiating ability and, thus, the organic materials used therein have had severe requirements in terms of electronic and physical properties as well as handling characteristics.
The adhesive tapes hitherto used for electronic parts in which a base film is necessarily required have had problems respective to fixation of lead pins and other application.
For example, in the case where the conventional adhesive is applied onto the base film is used in the fixation of lead pins in the conventionally developed resin-molded type semiconductor device (semiconductor package) as shown in FIG. 2, the heat resistance and electronic reliability are insufficient in some cases. In FIG. 2, lead pins 3 are locked by means of a locking tape 5, and connected with a semiconductor chip onto an island portion 4 via a bonding wire 7, which is molded with a molding resin 8. Also, in the case where a polyimide tape or a similar tape is applied, the conditions of temperature and pressure for taping and conditions for curing are severe so that the metal materials, such as leadframes, are damaged. Moreover, the conventional type of tape has been required to have a suitable area for applying a punch die and for ensuring a high level of accuracy, but accompanying the increase in the number of pins and down sizing, the necessary area has not been able to be ensured. For this reason, it has been required to develop a system and material which can be applied to an area narrower than the conventional area with a high level of accuracy and which is capable of innerlead lock.
Furthermore, dam bar 2 as shown in FIG. 1 is provided for the purpose of preventing the resin from being protruded during the course of transfer molding, and it is required to be cut off and removed thereafter. Moreover, accompanying the increase in the number of pins, the outer lead pitch become narrower, making it difficult to remove the metal dam bars themselves. For this reason, efforts have been made to use a conventional adhesive tape for electronic parts so as to be substituted for the metal dam bars, but due to the use of the polyimide based film, defects have occurred such as deformation of pins during molding.
Moreover, in the case of multi-layered leadframes, e.g., in the case of adhering a heat sink and leadframe while maintaining the insulation between them, a triple-layered tape in which a polyimide film is placed as a central layer, and an adhesive having high electronic reliability and little gas generation is adhered on the both sides has been used. Due to the complicated stages, however, it has been difficult to save cost. For this reason, it has been required to develop a liquid adhesive which can be used for adhering a heat sink and leadframe.
In addition, a double faced adhesive tape for electronic parts has been used for adhering lead pins and the body of a semiconductor chip such as in the case of an LOC structure and a COL structure, but the tape has problems in terms of the application of pressure and temperature onto the semiconductor chip during the course of taping and difficulty in saving cost.
Various adhesive tapes, adhesives, and organic insulating materials for use in electronic parts all have problems more or less.
In order to solve these problems, it has been, therefore, desired to develop a liquid adhesive for electronic parts which can be adhered and cured at a relatively low temperature, and possesses enough heat resistance, reliability, and processability.